Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Sorting out Ground Loop problem with Modded Oppo

I set up my player last night. Tested a few diff types of discs. DVD R4 works fine as do CDs. My only BD disc (all regions) plays ok. The SPDIF mod seems to work fine albeit minimal testing. Sound quality seems much better than my older DVD player on the few CDs I briefly tried.

I didn't get any codes to tell me what to type on the remote to use non-US BD discs - is this automatic now?

However, I have noticed 2 problems and I would appreciate any comments (I will also check with Gary as required):

1. With the Opop turned on at the powerpoint its sends a buzz and low-bass hum through the speakers when my power amp is on. Doesn't matter if the 568.2mm is on or off (at the back). With cables removed from the back of the Oppo, I don't get the noise, so it's getting out through the outputs. It was unbearable with the Oppo plugged in my power board. Straight to a wall socket, a bit better but still too loud and audible when sitting 3-4m away and generally unacceptable. Plugged into a socket across the room with an extension cord, its better but there is still a noise plus its not very practical.

I'm not sure what to do next - unsure why I am now getting this interferrence and how do I correct it. The back of the Oppo has a 220v sticker - of course we have 240v in Aust and I advised Gary of that. Perhaps he has no 240V stickers? In the event it is 220v would this perhaps be a cause?

2. I had the analogue outputs not disabled so I could use my headphone amp. The unit came with just the L and R stereo outputs active (the mod used the MCH outputs). CDs are fine, as was the PCM track of the BD I have. However, using the Spears BD test disc, the same BD (DTS track) and a DVD (DD track), when the Oppo is not reading an original PCM track, I get a static/ticking noise in the left channel. Presumably this is either a problem from the mod or a firmware issue?

I should note that I do not hear any of the hum etc through my headphone amp (same brand as my power amp).

Any help would be appreciated on the above points.

It sounds like you have a ground loop. This is usually caused by different devices using different grounding schemes.

In the USA some amps allow you to "Lift The Ground".

By plugging it in further and further away you're weaking the ground conflict (not a good solution).

You might be able add a device that isolates the ground.

Some people force the conflicting component to be ungrounded (by disconnecting it) which is not always the safest thing to do.

This is often why consumer devices elect to have no ground and build them "double insulated".

I don't know what the powersupply upgrade involved but if it added a ground that may point to the issue.

Just like an "argument" it takes TWO to disagree

Was the factory power supply universal (i.e. could it handle 220v?) Was it grounded? By the looks of images some look grounded and others do not and looks like it was universal. Personally I would have stuck with the factory power supply assuming it would work for you.

Thanks a alot George.

I am not that well informed on ground loop issues.

I believe the Oppos can do 115-240v (the manual refers to this) - the Digitial Edition mod by Gary, as I understand it, added an additional power supply.

I will need to have Gary advise on what changes were made to help diagnose the precise problem.

Mark, your unit is 220v only, just remove the ground plug on the amp, or run a ground wire between it and the Oppo and connect it on a screw on the outside of both chassis of the units

thanks

-Gary

Thanks for the response Gary.

Is it perhaps because it is 220v? Is it not possible to change to 240v as that is what we have in Australia?

I'm not sure really how to go about the grounding - I might contact my amp manufacturer here in Australia for their comments.

Gary - On the matter of the audio outpot from the stereo outputs, any comments on what may be causing that?

Thanks.

Try to turn the power plug 180 degrees. Sometimes it will help.
If the Oppo have a ground wire and you are familiar with a DVM, you can measure the ACvoltage between ground on the wall outlet and the chassis when you first remove the groundwire on the Oppo.
Then turn the power plug 180 defree and measure again.
The side with the lower voltage should be used.
Then mount the ground wire again on the chassis for safety reason,
if something breaks in your Oppo, you definetly have a bad accident-there is no joking here !!
You could do that with all your equipment,but normlly that not necssary as a good manufacturer have marked the hotline of your power or there is no influence at all.
But dont forget to plug the ground wire again !!
If all that doesnt help, you have to use "dehum" box what is actually a little isolation transformer in your signal line.

Robert that's a good idea on single phase but on 220v (in the usa any way) both legs are "hot" and flipping it "180 degrees" would make no change. 220v may be single phase (1 hot 1 neutral) in other countries I don't know.

Europe (most/all?) is live and neutral as is I understand Australia and New Zealand.

Mark, if you have ticking etc. with one track and not with PCM then that is probably a firmware issue of sorts, couldn't think of any other thing that would cause that

220v and 240v are the same thing, I gotta habit of calling 240v 220v

thanks

-Gary

Mark,

in case you haven't resolved your issue with the humming: please take a look at all cables that are connected to GROUND in some way. This could be any of the following types:
- power supply cables
- antenna cables
- connections to LAN/router/telephone

Now disconnect all cables that go either into the receiver/amp or the Oppo except:
- the 2 power supply cables (plug them into the same power block or 2 close wall sockets)
- the cables to the speakers
- the cables from the Oppo to the receiver/amp.

Do you still have the hum? If so then pull ONE power plug, turn it 180 degrees and put it back in (pins going into the other hole this time).

The hum should most likely be gone now.

If so then reconnect all the other parts of your hifi set one by one. Does the hum come back? After reconnecting which cable?

Good luck,
Thomas

Thanks. Is it typically "keyed" (i.e. you can only plug it in one way)?

No, British plugs are keyed but not standard European: